The role of protein kinase A in the ethanol-induced increase in spontaneous GABA release onto cerebellar Purkinje neurons.
Ethanol increases miniature inhibitory postsynaptic current frequency and decreases the paired-pulse ratio, which suggests that ethanol increases both spontaneous and evoked GABA release, respectively. We have shown previously that ethanol increases GABA release at the rat interneuron-Purkinje cell synapse and that this ethanol effect involves calcium release from internal stores; however, further exploration of the mechanism responsible for ethanol-enhanced GABA release was needed. We found that a cannabinoid receptor 1 (CB1) agonist, WIN-55212, and a GABA(B) receptor agonist, baclofen, decreased baseline spontaneous GABA release and prevented ethanol from increasing spontaneous GABA release. The CB1 receptor and GABA(B) receptor are Galpha i-linked G protein-coupled receptors with common downstream messengers that include adenylate cyclase and protein kinase A (PKA). Adenylate cyclase and PKA antagonists blocked ethanol from increasing spontaneous GABA release, whereas a PKA antagonist limited to the postsynaptic neuron did not block ethanol from increasing spontaneous GABA release. These results suggest that presynaptic PKA plays an essential role in ethanol-enhanced spontaneous GABA release. Similar to ethanol, we found that the mechanism of the cannabinoid-mediated decrease in spontaneous GABA release involves internal calcium stores and PKA. A PKA antagonist decreased baseline spontaneous GABA release. This effect was reduced after incubating the slice with a calcium chelator, BAPTA-AM, but was unaffected when BAPTA was limited to the postsynaptic neuron. This suggests that the PKA antagonist is acting through a presynaptic, calcium-dependent mechanism to decrease spontaneous GABA release. Overall, these results suggest that PKA activation is necessary for ethanol to increase spontaneous GABA release.
Kelm
M Katherine
MK
Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7178, USA. katie_kelm@med.unc.edu
Criswell
Hugh E
HE
Breese
George R
GR
D000818:Animals; D000831:Animals, Newborn; D001418:Baclofen / Q000494:pharmacology; D048588:Benzoxazines / Q000494:pharmacology; D001596:Benzylamines / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002492:Central Nervous System Depressants / Q000494:pharmacology*; D002531:Cerebellum / Q000166:cytology*; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation / Q000379:methods; D004791:Enzyme Inhibitors / Q000494:pharmacology; D000431:Ethanol / Q000494:pharmacology*; D018682:GABA Agents / Q000494:pharmacology; D066298:In Vitro Techniques; D053444:Inhibitory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009025:Morpholines / Q000494:pharmacology; D009281:Naphthalenes / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010721:Phosphinic Acids / Q000494:pharmacology; D011493:Protein Kinase C / Q000502:physiology*; D011689:Purkinje Cells / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D026941:Sodium Channel Blockers / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D048588:Benzoxazines; D001596:Benzylamines; D002492:Central Nervous System Depressants; D004791:Enzyme Inhibitors; D018682:GABA Agents; D009025:Morpholines; D009281:Naphthalenes; D010721:Phosphinic Acids; D026941:Sodium Channel Blockers; C083008:CGP 52432; D000431:Ethanol; D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid; C070417:(3R)-((2,3-dihydro-5-methyl-3-((4-morpholinyl)methyl)pyrrolo-(1,2,3-de)-1,4-benzoxazin-6-yl)(1-naphthalenyl))methanone; D011493:Protein Kinase C; D001418:Baclofen; D002118:Calcium